const USER_AGENT = 'shiroko-monitor/0.2 (lightweight uptime panel)';

export async function probeHttp(monitor) {
  const started = Date.now();
  const timeoutMs = (monitor.timeout ?? 10) * 1000;
  try {
    // redirect: manual —— 保留 3xx 原始状态码交给 expectStatus 判定，避免跟随重定向掩盖异常
    const res = await fetch(monitor.url, {
      method: monitor.method || 'GET',
      redirect: 'manual',
      signal: AbortSignal.timeout(timeoutMs),
      headers: { 'user-agent': USER_AGENT, accept: '*/*' },
    });
    const latency = Date.now() - started;
    const expect = monitor.expectStatus ?? [200];
    const ok = expect.includes(res.status);
    return {
      status: ok ? 'up' : 'down',
      latency,
      code: res.status,
      detail: ok ? `HTTP ${res.status}` : `HTTP ${res.status}（期望 ${expect.join('/')}）`,
    };
  } catch (err) {
    const latency = Date.now() - started;
    let detail;
    if (err.name === 'TimeoutError') detail = `请求超时（>${timeoutMs / 1000}s）`;
    else if (err.cause?.code) detail = err.cause.code;
    else detail = err.message;
    return { status: 'down', latency, code: 0, detail };
  }
}